The lgt11 expression system is a powerful tool employed by researchers in order to identify and express genes of interest. Our laboratory has generated three mycobacterial gene expression libraries in an effort to identify antigens which may be useful in the diagonsis of mycobacterial diseases or as components of vaccines. The libraries have also been used to identify mycobacterial proteins and lipoproteins which may provide further insight into the pathogenesis of mycobacteria. We have generated a M. avium lgt11 gene expression library from a strain of M. avium isolated from an AIDS patient. This same strain of M. avium was also used to generate 25 monoclonal antibodies, several of which are serologically specific for M. avium or M. avium complex (MAC) antigens. These monoclonal antibodies (MAbs) have been used to identify recombinant bacteriophages from the M. avium library expressing epitopes found on the 26, 30, 33, and 70 kDa M. avium antigens and to identify clones from the M. intracellulare library expressing recombinant proteins corresponding to 34 and 70 kDa antigens. These recombinant antigens are currently undergoing purification using HPLC techniques. One of the two antigens which have been purified thus far (MA26) has been shown to elicit a strong skin test response in sensitized animals. In addition to screening the M. avium library, studies have been initiated to determine if any of these MAbs are directed against epitopes found on mycobacterial heat shock proteins (HSPs). Several studies have shown that mycobacterial HSPs, particularly HSP65 from M. tuberculosis, may play an important role in autoimmune diseases such as rheumatoid arthritis. One of the MAbs (3954) has been shown to recognize an aberrant form of ~- galactosidase generated by the lgt11 system. This MAb may be useful for identifying fusion proteins which do not conform to predicted molecular sizes and reactivities.